a) Field of the Invention
This invention relates to an electrically conductive polymer type copper composition for use in forming film circuits, and more particularly to a conductive copper composition having a good solderability as well as a high conductivity formed by using copper powder in spherical or granular particles coated with silver as a metal powder and a resol-type phenolic resin as a binder.
b) Description of the Prior Art
Good solderability is required for conductive polymer type copper compositions used in forming film circuits in order to facilitate soldering of lead wires, pins, and the like. A conductive copper composition having its solderability taken into consideration is known from Japanese Patent Provisional Publication gazette No. 34597/1989. The composition of the invention disclosed by the gazette comprises metal powder, a resol resin, a saturated or unsaturated fatty acid, or a metal salt thereof, a metal chelate forming agent, and a soldering accelerating agent. This formulation provides the composition with a good solderability by the addition of the metal chelate forming agent for inhibiting oxidation of the metal powder and the soldering accelerating agent.
However, there are problems with such compositions heretofore proposed, such as the one mentioned above, that they require the addition of antioxidants for inhibiting the oxidation of metal powder and a soldering accelerating agent and that their electrical conductivity is not sufficient, despite their good solderability, while and the solderability of compositions proposed with principal regard to the conductivity is not sufficient. Thus, there are no compositions which both conductivity and solderability required for formed film. Accordingly, circuit patterns must be formed by the combined use of compositions with good conductivity and compositions with good solderability, or by plating printed patterns of copper paste with a metal by means of electroless deposition.
The former method requires extra steps which make the process more complicated and increase the cost, while the latter method has the problem of the disposal of waste liquid which causes a substantial cost increase.